In many industrial situations there is a need to protect the workers from the surrounding atmosphere. This is especially true when workers are forced to work inside large vessels such as chemical reactors or petroleum crackers. The atmosphere in which the worker is forced to work may be low in oxygen or could be immediately hazardous to life (contain poisonous gases) and in such situations the workers are required to wear air-purifying or atmosphere-supplying respirators.
The preferred type of protection for situations where the atmosphere is immediately hazardous to life and health or when the contaminant has poor warning properties is the atmosphere-supplying respirator. There are two general types of atmosphere-supplying respirators: (1) self-contained breathing apparatus, where the wearer carries his oxygen supply with him and (2) supplied-air apparatus, where the oxygen source is stationary and attached to the respirator wearer by a flexible hose.
The self-contained breathing apparatus can be either a closed-circuit or an open-circuit type. With a closed-circuit system the wearer's exhaust gases are passed through a system for removing the carbon dioxide and replenishing the used oxygen. The wearer "rebreathes" part of the original gases.
The open-circuit breathing apparatus is one where the wearer exhales used gases into the surrounding atmosphere. Open-circuit self-contained breathing systems and supplied air systems are similar in that both are available as either "demand" or "pressure-demand" systems.
An open-circuit demand system has a regulator which has an admission valve which is closed as long as positive pressure is maintained in the face plate. Inhalation (or demand) opens the admission valve to admit oxygen containing gases.
The pressure-demand system is very similar except there is always a positive pressure of breathing gas within the mask. The gases would continually flow out of the face piece except in a pressure-demand system there is a special exhalation or exhaust valve that maintains about 1-3 inches of water positive pressure in the face piece. This exhalation valve opens only when the pressure exceeds the backpressure, i.e., when the wearer exhales.
The open-circuit pressure-demand full face piece system is considered the system which gives the maximum protection, yet the system is no better than the reliability of the special exhalation valve. The exhalation valve fits into the face piece and is subject to a number of things which may cause it to malfunction. Dirt and debris can get into the exhalation valve and lodge between the valve and the seat preventing it from closing or dirt could get in the stem hole and prevent the valve from opening and/or closing. This is especially true when (because of ice or dirt) the pressure is not applied uniformly across the valve face causing the valve stem to stick in the stem hole. The improved exhalation valve of the present invention overcomes these disadvantages of the existing valves and offers a number of new advantages.